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Cambridge International Examinations
Cambridge International Advanced Subsidiary and Advanced Level
*8715689080*
CHEMISTRY
9701/34
Paper 3 Advanced Practical Skills 2
May/June 2014
2 hours
Candidates answer on the Question Paper.
Additional Materials:
As listed in the Confidential Instructions
READ THESE INSTRUCTIONS FIRST
Write your Centre number, candidate number and name on all the work you hand in.
Give details of the practical session and laboratory where appropriate, in the boxes provided.
Write in dark blue or black pen.
You may use an HB pencil for any diagrams or graphs.
Do not use staples, paper clips, glue or correction fluid.
DO NOT WRITE IN ANY BARCODES.
Answer all questions.
Electronic calculators may be used.
You may lose marks if you do not show your working or if you do not use appropriate units.
Use of a Data Booklet is unnecessary.
Session
Qualitative Analysis Notes are printed on pages 11 and 12.
At the end of the examination, fasten all your work securely together.
The number of marks is given in brackets [ ] at the end of each question or
part question.
Laboratory
For Examiner’s Use
1
2
3
Total
This document consists of 12 printed pages.
IB14 06_9701_34/5RP
© UCLES 2014
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1
You are to determine the percentage of calcium carbonate in a sample of crushed limestone. You
will first react a known mass of the crushed limestone in a known amount of hydrochloric acid,
HCl (aq), to make a solution. You may assume that only the calcium carbonate present in the
sample will react with the acid.
CaCO3(s) + 2HCl (aq) → CaCl 2(aq) + H2O(l) + CO2(g)
The amount of acid that did not react with the carbonate is then found by a titration using sodium
hydroxide. You may assume that no compounds present in the limestone will react with the sodium
hydroxide.
NaOH(aq) + HCl (aq) → NaCl (aq) + H2O(l)
FB 1 is crushed limestone, impure calcium carbonate.
FB 2 is 2.0 mol dm–3 hydrochloric acid, HCl.
FB 4 is 0.20 mol dm–3 sodium hydroxide, NaOH.
methyl orange indicator
(a) Method
Read through the method before starting any practical work.
Making the solution
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© UCLES 2014
Weigh the container with the limestone, FB 1, and record the mass below.
Tip all the solid FB 1 into a 250 cm3 beaker.
Reweigh the container and record the mass.
Fill the burette with FB 2.
Slowly run between 47.5 and 48.5 cm3 of FB 2 into the beaker containing FB 1.
Record, in the space below, both your burette readings and the volume of FB 2 added.
Stir the mixture carefully until all the solid has reacted.
Transfer the contents of the beaker into the volumetric flask.
Rinse the beaker with distilled water and add it to the volumetric flask. Make the solution
up to 250 cm3 with distilled water and mix thoroughly. This is solution FB 3.
9701/34/M/J/14
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Titration
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Empty and rinse the burette with distilled water.
Fill the burette with FB 3 from the volumetric flask.
Pipette 25.0 cm3 of FB 4 into a conical flask.
Add a few drops of methyl orange indicator.
Perform a rough titration and record your burette readings in the space below.
The rough titre is ...................... cm3.
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Carry out as many accurate titrations as you think necessary to obtain consistent results.
Make certain any recorded results show the precision of your practical work.
Record, in a suitable form below, all of your burette readings and the volume of FB 3
added in each accurate titration.
I
II
III
IV
V
VI
VII
VIII
IX
[9]
(b) From your accurate titration results, obtain a suitable value to be used in your calculations.
Show clearly how you have obtained this value.
25.0 cm3 of FB 4 required ................ cm3 of FB 3. [1]
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(c) Calculations
Show your working and appropriate significant figures in the final answer to each step of your
calculations.
(i) Calculate the number of moles of sodium hydroxide present in 25.0 cm3 of FB 4.
moles of NaOH = ....................... mol
(ii) Hence state the number of moles of hydrochloric acid present in the volume of FB 3
calculated in (b).
moles of HCl = ....................... mol
(iii) Use your answer to (ii) to calculate the number of moles of hydrochloric acid present in
250 cm3 of FB 3.
moles of HCl in 250 cm3 of FB 3 = ....................... mol
(iv) Calculate the number of moles of hydrochloric acid, FB 2, added to FB 1 in (a).
moles of HCl added to FB 1 = ....................... mol
(v) Use your answers to (iii) and (iv) to calculate the number of moles of hydrochloric acid that
reacted with the calcium carbonate in FB 1.
I
II
III
IV
moles of HCl reacted with CaCO3 = ....................... mol
(vi) Calculate the number of moles of calcium carbonate present in your sample of FB 1.
V
VI
VII
moles of CaCO3 = ....................... mol
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(vii) From your answer to (vi) and the mass of FB 1 used in (a), calculate the percentage by
mass of calcium carbonate in the limestone.
[Ar: C, 12.0; O, 16.0; Ca, 40.1]
percentage of calcium carbonate = ................... %
[7]
(d) (i) The maximum error in a single burette reading is ±0.05 cm3.
Student X, carrying out this experiment, recorded that 48.50 cm3 of FB 2 was added to
FB 1.
What are the smallest and largest possible volumes of FB 2 that were added?
smallest volume used = .................. cm3
largest volume used = .................. cm3
(ii) Student Y used an identical mass of FB 1 but added 47.70 cm3 of FB 2. How would the
value obtained in (b) by student X compare with the value obtained by student Y?
Explain your answer.
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[3]
[Total: 20]
© UCLES 2014
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2
You are to determine the percentage by mass of calcium carbonate in another sample of the
limestone by thermal decomposition. You may assume that none of the other compounds in the
limestone sample is affected by heating. The equation for the reaction that occurs is given below.
CaCO3(s) → CaO(s) + CO2(g)
FB 5 is crushed limestone, impure calcium carbonate.
(a) Method
Read through the method before starting any practical work and prepare a table for your
results in the space below.
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Weigh the empty crucible and record the mass in your table.
Transfer all the FB 5 into the crucible.
Weigh the crucible with FB 5 and record the mass.
Place the crucible on the pipe-clay triangle.
Heat the crucible gently for about one minute and then strongly for three minutes.
Remove the Bunsen burner and allow the crucible to cool.
While the crucible is cooling start working on another question.
Reweigh the cooled crucible with contents and record the mass.
Reheat the crucible strongly for three minutes, cool and reweigh. Record the mass.
Record the mass of FB 5 used and the mass of solid remaining after the second heating.
[2]
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(b) Calculations
Show your working and appropriate significant figures in the final answer to each step of your
calculations.
(i) From your results in (a), calculate the total mass of carbon dioxide lost on heating FB 5.
mass of CO2 lost = ................ g
(ii) Use your answer to (i) to calculate the mass of calcium carbonate present in the sample
of FB 5 heated.
[Ar: C, 12.0; O, 16.0; Ca, 40.1]
mass of CaCO3 = .................. g
(iii) Calculate the percentage by mass of calcium carbonate in the limestone.
percentage of calcium carbonate = ................. %
[3]
(c) FB 5 and FB 1 are samples of the same limestone. You have determined the percentage of
calcium carbonate in both Questions 1 and 2 using two different procedures.
(i) Which procedure is the less accurate? Explain your answer.
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(ii) Suggest a change to the less accurate practical procedure that would improve the accuracy
and explain your answer.
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[2]
[Total: 7]
© UCLES 2014
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3
Qualitative Analysis
At each stage of any test you are to record details of the following.
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colour changes seen
the formation of any precipitate
the solubility of such precipitates in an excess of the reagent added
Where gases are released they should be identified by a test, described in the appropriate place
in your observations.
You should indicate clearly at what stage in a test a change occurs.
Marks are not given for chemical equations.
No additional tests for ions present should be attempted.
If any solution is warmed, a boiling tube MUST be used.
Rinse and reuse test-tubes and boiling tubes where possible.
Where reagents are selected for use in a test, the name or correct formula of the
element or compound must be given.
(a) A different sample of limestone was reacted with dilute nitric acid to give solution FB 6.
This sample of limestone contained calcium carbonate, CaCO3, and one other salt.
This additional salt contains a single cation and a single anion from those listed on pages 11
and 12. By carrying out the following tests you will be able to suggest identities of the additional
ions.
test
observations
(i) To a 1 cm depth of FB 6 in a test-tube
add aqueous ammonia.
(ii) To a 1 cm depth of FB 6 in a test-tube
add a 1 cm depth of aqueous silver
nitrate.
(iii) To a 1 cm depth of FB 6 in a test-tube
add a 1 cm depth of aqueous barium
chloride or barium nitrate.
© UCLES 2014
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(iv) Suggest all possible identities for the ions present in FB 6, apart from Ca2+ and NO3–.
.............................................................................................................................................
(v) Select a reagent to use in a further test on FB 6 to confirm that one of the cations you have
listed in (iv) is not present in FB 6. Carry out your test and complete the table.
test
observations
conclusion
To a 1 cm depth of FB 6 in
a test-tube add
.........................................
I
[6]
II
III
IV
V
VI
(b) You are provided with a solid, FB 7. By carrying out the following tests you will be able to
identify three of the ions present in FB 7.
test
observations
(i) Place a spatula measure of FB 7 in
a hard-glass test-tube. Heat gently at
first, then
heat more strongly until no further
change is seen, then
allow the tube to cool.
© UCLES 2014
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10
test
observations
(ii) Place a spatula measure of FB 7 in a
test-tube.
Add about a 5 cm depth of dilute
nitric acid.
You will use the solution formed for
tests (iii) to (v).
(iii) To a 1 cm depth of the solution in a
test-tube add a few drops of aqueous
potassium manganate(VII), then
I
II
III
IV
add a few drops of starch solution.
V
VI
VII
(iv) To a 1 cm depth of the solution in a
test-tube add a few drops of aqueous
silver nitrate.
(v) To a 1 cm depth of the solution in a
test-tube add aqueous ammonia.
Use the Qualitative Analysis Notes on pages 11 and 12 to identify three of the ions present.
....................................................................................................................................................
[7]
[Total: 13]
© UCLES 2014
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11
Qualitative Analysis Notes
Key: [ppt. = precipitate]
1
Reactions of aqueous cations
ion
reaction with
NH3(aq)
NaOH(aq)
aluminium,
Al 3+(aq)
white ppt.
soluble in excess
white ppt.
insoluble in excess
ammonium,
NH4+(aq)
no ppt.
ammonia produced on heating
–
barium,
Ba2+(aq)
no ppt. (if reagents are pure)
no ppt.
calcium,
Ca2+(aq)
white ppt. with high [Ca2+(aq)]
no ppt.
chromium(III),
Cr3+(aq)
grey-green ppt. soluble in excess
giving dark green solution
grey-green ppt.
insoluble in excess
copper(II),
Cu2+(aq)
pale blue ppt.
insoluble in excess
blue ppt. soluble in excess
giving dark blue solution
iron(II),
Fe2+(aq)
green ppt. turning brown on contact
with air
insoluble in excess
green ppt. turning brown on contact
with air
insoluble in excess
iron(III),
Fe3+(aq)
red-brown ppt.
insoluble in excess
red-brown ppt.
insoluble in excess
magnesium,
Mg2+(aq)
white ppt.
insoluble in excess
white ppt.
insoluble in excess
manganese(II),
Mn2+(aq)
off-white ppt. rapidly turning brown
on contact with air
insoluble in excess
off-white ppt. rapidly turning brown
on contact with air
insoluble in excess
zinc,
Zn2+(aq)
white ppt.
soluble in excess
white ppt.
soluble in excess
© UCLES 2014
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2
Reactions of anions
ion
carbonate,
reaction
CO2 liberated by dilute acids
2–
CO3
chloride,
gives white ppt. with Ag+(aq) (soluble in NH3(aq));
Cl –(aq)
bromide,
gives cream ppt. with Ag+(aq) (partially soluble in NH3(aq));
–
Br (aq)
iodide,
gives yellow ppt. with Ag+(aq) (insoluble in NH3(aq));
I (aq)
–
nitrate,
NH3 liberated on heating with OH–(aq) and Al foil
NO3–(aq)
NH3 liberated on heating with OH–(aq) and Al foil;
nitrite,
NO2–(aq)
NO liberated by dilute acids
(colourless NO → (pale) brown NO2 in air)
sulfate,
gives white ppt. with Ba2+(aq) (insoluble in excess dilute strong acids)
SO42–(aq)
SO2 liberated with dilute acids;
sulfite,
2–
gives white ppt. with Ba2+(aq) (soluble in excess dilute strong acids)
SO3 (aq)
3
Tests for gases
gas
test and test result
ammonia, NH3
turns damp red litmus paper blue
carbon dioxide, CO2
gives a white ppt. with limewater
(ppt. dissolves with excess CO2)
chlorine, Cl 2
bleaches damp litmus paper
hydrogen, H2
“pops” with a lighted splint
oxygen, O2
relights a glowing splint
sulfur dioxide, SO2
turns acidified aqueous potassium manganate(VII) from purple to
colourless
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Cambridge International Examinations is part of the Cambridge Assessment Group. Cambridge Assessment is the brand name of University of Cambridge Local
Examinations Syndicate (UCLES), which is itself a department of the University of Cambridge.
© UCLES 2014
9701/34/M/J/14